1. Field of the Invention
The present invention relates to a peripheral surface shape measuring apparatus of a roll-like object, and more particularly, relates to a peripheral surface shape measuring apparatus of a roll-like object which measures a peripheral surface shape of a huge roll-like object such as a magnetic tape bulk roll and judges whether or not the peripheral surface of the roll-like object has a poor shape such as a curve.
2. Related Art
Magnetic tapes are made by cutting a wide magnetic tape bulk roll into tapes with the same narrow width. However, in roll forming of a magnetic tape bulk roll, a winding force at both ends of the magnetic tape bulk roll is slightly different from a winding force at the center, and thus, the roll peripheral surface often has a shape such that the center swells like a curve along an axial direction of the roll.
Another factor for such a peripheral surface shape is that a raw magnetic tape is coated, wound and then stored for a long time, and thus subjected to plastic deformation.
A magnetic tape obtained from the magnetic tape bulk roll having the peripheral surface shape such that the center greatly swells like a curve does not have a linear shape but has a curved shape. The use of such a magnetic tape having a curved shape causes poor electrical output or the like and lowers reliability as a product. Thus, coating with as even thickness as possible is required for preventing such a defect.
On the other hand, in view of improvement in productivity, providing thick coating at the center is also required for more stable conveyance as disclosed in Japanese Patent Application Laid Open No. 61-293577. This causes winding tension to act more strongly on ends than the center to stabilize winding when the raw magnetic tape is wound around a winding core. This can prevent defects such as winding displacement or longitudinal wrinkles.
As described above, in order to satisfy both the contradictory requirements of “the coating with the even thickness” and “the thick coating at the center”, extremely accurate thickness adjustment is required. This requires precise measurement of the shape of the magnetic tape bulk roll before cutting of the magnetic tape bulk roll.
Particularly, in recent years, the width of a recording track has become increasingly narrower with higher densities of a magnetic recording medium, and thus higher dimensional accuracy of a magnetic tape bulk roll and a medium (a magnetic tape) has been required.
Various methods for measuring the shape of a magnetic tape bulk roll have been proposed (Japanese Patent Application Laid Open No. 8-102064 and Japanese Patent Application Laid Open No. 2002-168616, or the like).
Japanese Patent Application Laid Open No. 8-102064 discloses an apparatus which measures the shape of a magnetic tape bulk roll using a contact sensor that runs in parallel with a core of the magnetic tape bulk roll.
Japanese Patent Application Laid Open No. 2002-168616 discloses an apparatus which measures the shape of a magnetic tape bulk roll using a contact sensor that pinches the magnetic tape bulk roll from both sides.